Rho is a protein required for the release of nascent RNA transcripts from a large number of transcription complexes in both gram-negative and gram-positive bacteria. In vitro, Rho binds single stranded DNA and RNA, but preferential activation of helicase activity by cytidine-containing oligoribonucleotides leads to termination of transcription. Since Rho protein plays a central role in the regulation of protein synthesis it is a significant and essential component of bacterial metabolism. Information about Rho-nucleic acid interactions at the atomic level may be of potential aid in the development of novel anti-bacterial agents. Within the past decade the nucleic acid binding properties, enzymology, and regulatory properties of this important protein have been the subject of intense studies by a number of investigators. Additionally, a large number of mutations of this protein have been made in an effort to understand the mechanism of Rho. Although this work has lead to significant advances in our understanding of Rho function, these advances have not been able to address the mechanism at the atomic level because there is no information on the structure of Rho at this level. The proposed research will investigate the structure of the RNA binding domain of Rho, a 15kDa fragment which has been expressed in E. coli. Both the NMR solution structure and the x-ray crystallographic structure of this domain will be determined in the presence and absence of various RNA and DNA oligonucleotides. The site size and binding constant for the binding of DNA and RNA oligonucleotides to this domain of Rho will be evaluated. Analysis of this binding data, in conjunction with the atomic structure of the RNA binding domain, will provide a new perspective in the understanding of Rho function. Further, since Rho contains a novel RNA-binding motif, these studies will also greatly enhance knowledge of RNA-protein interactions in general.